1. Field of the Invention
The present invention relates to an integrated optical coupler and housing arrangement, and in particular, to a housing and integrated optical coupler arrangement that is used to optically couple and align a light emitter or light detector with an optical fiber connector.
2. Background Information
Computer and communication systems are now being developed in which optical devices, such as optical fibers, are used as a conduit (also known as a wave guide) for modulated light waves to transmit information. These systems typically include a light emitter or a light detector optically connected to the optical fibers. A typical light emitter may be a so-called edge emitter, or a surface emitter, such as a vertical cavity surface emitting laser (VCSEL). A typical light detector may be a photodiode. A generic term of either a light emitter or a light detector is an xe2x80x9coptoelectronic transducer.xe2x80x9d The optical fibers, which collectively form a fiber-optic cable or ribbon, are typically coupled to the respective light detector and the light emitter, so that optical signals can be transmitted back and forth, for example.
As an example, optoelectronic transducers convert electrical signals to or from the optical signals; the optical signals carry data to a receiver (light detector) from a transmitter (light emitter) via the fiber-optic ribbon at very high speeds. Typically, the optical signals are converted into, or converted from, the associated electrical signals using known circuitry. Such optoelectronic transducers are often used in devices, such as computers, in which data must be transmitted at high rates of speed.
The conventional light emitter allows for integrated two-dimensional array configurations. For example, the active regions (i.e., the region that transmits or receives the optical signals) of a conventional VCSEL can be arranged in a linear array, for instance 12 active regions spaced about 250 microns apart, or in area arrays, for example, 16xc3x9716 arrays or 8xc3x978 arrays. Of course, other arrangements of the arrays are also possible. Nevertheless, linear arrays are typically considered to be preferable for use with optoelectronic transducers, since it is generally considered easier to align the optical fibers that collect the light emitted from the VCSELs in a linear array, than in an area array. Moreover, it is also possible to utilize the active regions singly, i.e., without being arranged in an array.
The optoelectronic transducers are normally located on either input/output cards or port cards that are connected to an input/output card. Moreover, in a computer system, for example, the input/output card (with the optoelectronic transducer attached thereto) is typically connected to a circuit board, for example a mother board. The assembly may then be positioned within a chassis, which is a frame fixed within a computer housing. The chassis serves to hold the assembly within the computer housing.
Typically, each optical fiber of the fiber-optic ribbon is associated with a respective active region. Further, it is conventional for the ends of the optical fibers of the fiber-optic ribbon to terminate in a fiber connector. Such fiber connectors usually have an industry standard configuration, such as the MTP(copyright) fiber connectors manufactured by US Conec, Ltd. of Hickory, N.C. However, fiber connectors having the industry standard configuration are not suitable for connecting directly with the sensitive active regions of the typical light emitters or light detectors. Should direct contact occur between the respective active regions and the fiber connector, the fiber connector would likely damage the active regions, causing the light emitter or light detector to become inoperative. It is thus conventional to space the fiber connector away from the active regions. However, as will be appreciated, by providing a space, it thus becomes desirable to provide a way of optically coupling the active regions with the spaced apart fiber connector, so that the optical signals can be accurately and efficiently transmitted therebetween.
One conventional manner of optically coupling the active regions with the fiber connector is to provide a lens assembly in the space therebetween. However, lens assemblies tend to be complicated and expensive. Thus, it is also known to provide a fiber optic coupler between the active regions and the fiber connector. However, the conventional fiber optic coupler has a limited length, due to manufacturing constraints. Thus, the known fiber connectors must be positioned relatively close to the active regions, which may limit design options.
Moreover, it is important to ensure that most of the light emitted from the active regions of the light emitter reaches the respective optical fibers, and that most of the light emitted from the optical fibers reaches the respective active regions of the light detector. It is thus desirable to ensure that the fiber optic coupler is precisely aligned with the respective active regions and the fiber ends disposed within the fiber connector.
It is also known to dispose the optical coupler within a housing, which is adapted to receive the optical connector in a manner that automatically aligns the optical fibers terminating at the optical connector with the optical coupler. The housing also allows the optical coupler to be fixed relative to the light emitter and/or light detector. That is, after the optical coupler is aligned with the respective active regions, the optical coupler may be fixed to the housing using a bonding agent, for example. However, the application of the bonding agent requires further steps during the manufacturing of the arrangement, thus increasing assembly time. Moreover, the bonding agent could inadvertently be applied to the optical face of the optical coupler, or to the active regions, thus damaging the assembly.
Thus, there is a need for an optical coupler/housing arrangement that allows the optical coupler to be fixed relative to the housing without requiring an extra bonding step, or a separate bonding agent.
Furthermore, the conventional optical coupler is typically freely positionable within the housing, prior to the application of the conventional bonding agent. For example, the housing may be provided with a channel, with the optical coupler being disposed in the channel. In order to ensure that the optical coupler can be positioned within the housing, the outer periphery of the optical coupler is made slightly smaller than an inner periphery of the channel, so that the optical coupler fits within the channel with a clearance fit. However, it must also be ensured that when the optical connector is connected to the housing, the optical coupler is aligned with the optical fibers that terminate at the optical connector. Thus, both the channel within the housing, and the optical coupler must be manufactured using relatively strict tolerances. That is, if the optical coupler is made as large as the tolerances allow, and the channel is made as narrow as the tolerances allow, the optical coupler must still be capable of fitting within the channel with a clearance fit. Moreover, once received within the channel, there cannot be too much free play, or the optical coupler may not be properly aligned with the optical fibers terminating at the optical connector. Manufacturing these components while maintaining the required tolerances is expensive and time consuming. Thus, there is a need for an optical coupler and housing arrangement that can be manufactured without regard to the tolerances discussed above.
It is, therefore, a principle object of this invention to provide an integrated optical coupler and housing arrangement.
It is another object of the invention to provide an integrated optical coupler and housing arrangement that solves the above mentioned problems.
These and other objects of the present invention are accomplished by the integrated optical coupler and housing arrangement disclosed herein.
According to one aspect of the invention, the integrated optical coupler and housing arrangement includes an optical coupler portion. The optical coupler portion optically couples active regions of a light emitter die chip or light detector die chip with the fibers within a fiber optic connector (i.e., an industry standard connector attched to an end of an optical fiber ribbon), so that the optical signals can be accurately and efficiently transmitted therebetween.
The integrated optical coupler and housing arrangement further includes a housing portion that has a recess for receiving the fiber optic connector, and which is adapted to selectively receive either the MPO or MTP industry standard connector, for example. A back surface of the recess is defined by an end surface of the optical coupler portion. Thus, when the fiber optic connector is received within the recess, the optical fibers of the optical coupler portion will be positioned adjacent to the fiber optic connector.
The housing portion may also be provided with a pair of latching fingers disposed on opposite sides of the recess. The latching fingers are adapted to engage with the fiber optic connector, to hold the connector in place.
In an exemplary aspect of the invention, the housing portion and the optical coupler portion are formed from a filled polymer, i.e., a polymer that includes a glass filler. In an exemplary aspect of the invention, the polymer has a glass content of about 30%. This content has proven to be particularly suitable when manufacturing the housing portion and the optical coupler portion using the molding techniques discussed in the following paragraphs.
In particular, in an exemplary aspect of the invention, the housing portion and the optical coupler portion are manufactured using an injection molding technique. The optical coupler portion, if injection molded, can be made to have any desired length. That is, the optical fibers, of any desired length, may be prearranged in their desired locations, and then the filled polymer would be injected around the fibers to form the optical coupler portion. This exemplary procedure is further advantageous in that, since the optical fibers do not need to be inserted within holes preformed in the optical coupler, the optical fibers will not be subjected to damage during such a procedure. Moreover, because the injection molding procedure also inherently fixes the optical fibers in their desired locations, there is no need for a separate bonding procedure to fix the optical fibers in place. Additionally, since a separate bonding agent is not needed to fix the optical fibers within the optical coupler portion, there is a reduced risk of the optical fibers being damaged due to the boding agent inadvertently contacting the optical fibers or other components.
This exemplary aspect of the invention also eliminates the need for a subsequent polishing step to the end faces of the optical fibers. That is, if the optical fibers are inserted within the holes of an optical coupler, the end faces would subsequently need to be polished, so as to remove any scratches or contaminates that may have formed on the end faces during the insertion procedure, and to ensure that all of the end faces are disposed in essentially the same plane and at essentially the same relative angle. However, when the optical fiber portion is formed by injection molding, the end faces of the optical fibers are not subjected to treatment after assembly that may cause damage thereto. Moreover, the end faces can be prealigned, so that even after the formation of the optical fiber portion, the end faces are in their desired aligned orientation.
The exemplary described technique used for forming the optical coupler portion can also be used to simultaneously form the housing portion, so that the optical coupler portion and the housing portion are integrally formed. This reduces the number of separate components that must otherwise be formed. Further, this technique eliminates the need to manufacture the mating surfaces of the housing and optical coupler using exacting tolerances, thus speeding up production. Additionally, this procedure eliminates the need to separately adhere the optical coupler to the housing, thus reducing the number of manufacturing steps, and reducing the risk of contamination to the components from bonding agents.
In another exemplary aspect of the invention, the housing portion and fingers are molded to have a one-piece configuration. This reduces assembly time by eliminating the need to fix separate latching fingers to the housing, and reduces inventory by eliminating multiple parts.
In another exemplary aspect of the invention, the integrated optical coupler and housing arrangement can include first and second housing portions disposed side-by-side, each of which has an optical coupler portion integrally formed therewith. This configuration allows both a light emitter and a light detector, for example, to be disposed in the same assembly, therefore saving circuit board space. The respective housings can be manufactured separately and joined together, for example, or the two housings can be integrally molded together.
In another exemplarily aspect of the invention, the front end of the integrated optical coupler and housing arrangement may also be provided with an electromagnetic interference shield. The electromagnetic interference shield is preferably formed from a conductive, non-corrosive material, such as steel having a tin plating. However, the electromagnetic interference shield can be formed of any material that will attenuate electromagnetic interference.
The electromagnetic interference shield may be hollow, to allow the shield to be slipped over the front end of the integrated optical coupler and housing arrangement. When properly positioned, the edge of the electromagnetic interference shield will be positioned essentially flush with the front end of the housing portion. The shield may be provided with inwardly projecting fingers that engage with the surface of the housing portion, to hold the shield in place.
In another exemplary aspect of the invention, the electromagnetic interference shield is provided with a number of conductive grounding springs, which are disposed around the outer periphery of an end of the shield. The grounding springs engage, for example, with a tailstock attached to a system frame of a computer, for example, to conductively couple the electromagnetic interference shield to a ground potential. When properly positioned, the grounding springs hold the electromagnetic interference shield in a fixed position relative to the tailstock.
The shield can advantageously be used to hold the first and second housing portions together, when two separate housing portions are provided. That is, the shield can be slid around the adjacent housing portions, and serve as a clamp to retain the housing portions in their relative positions.
In an exemplary aspect of the invention, the integrated optical coupler and housing arrangement forms a component of an optical transceiver arrangement that includes a plurality of other interconnected subassemblies.
One of the subassemblies of the optical transceiver arrangement is a carrier assembly. The carrier assembly includes a die carrier for carrying a die chip, having opposing lands. The opposing lands have a receiving space therebetween, in which either a light emitter die chip or light detector die chip (hereinafter referred to collectively as a die chip) is disposed.
The carrier is preferably manufactured from a conductive material, so that it can serve as a ground for the die chip. For example, the carrier can be formed from copper, and be gold plated to enhance its conductivity and reduce its susceptibility to oxidation.
The carrier further has spaced apart feet, which can be attached to a further subassembly of the optical transceiver arrangement, as will be subsequently described. The feet provide a space under the carrier in which other components can be disposed.
The lands are adapted to allow an optical coupler to be attached thereto. For example, each land can be provided with a receiving hole, which receives a corresponding alignment pin of the optical coupler in a clearance type fit.
In another exemplary aspect of the invention, an epoxy, for example, can be used to seal the exterior edges of the optical coupler portion to the surface of the die chip. The epoxy may have a sufficiently high viscosity so as to prevent the epoxy from flowing into the gap between the front edge of the optical coupler portion and the active regions of the die chip. Thus, a sealed air gap will be formed between the ends of the optical fibers in the optical coupler portion and the active regions to allow for the efficient transmission of light, while preventing contaminants from entering this space.
In a further exemplary aspect of the invention, the carrier assembly includes a flex cable that is electrically coupled to the die chip. The flex cable has both ground wires (or a ground layer) and signal wires which may be covered by an insulating coating, such as plastic. The insulating coating may be removed in a region at one end of the flex cable, to form one or more windows which expose the signal wires, grounds wires or both as they pass through the space of the windows. For example, if the flex cable is provided with two windows, one disposed over the other, the lower window can be adapted to expose the ground wires, to allow the ground wires to be electrically coupled to the conductive carrier. The upper window can then be adapted to expose the signal wires, which can then be electrically coupled to the die chip. This arrangement works well when the die chip is attached and directly grounded to the carrier.
Alternatively, if the die chip is not directly grounded to the carrier, then the flex cable can be provided with only one window, which is adapted to expose both the ground wires and the signal wires. These can then be electrically coupled to the die chip, for example a light detector die chip, to provide both a signal path and a return ground path.
Another end of the flex cable may be provided with a conductive plate, such as a metal stiffener, electrically bonded to the ground wires/ground layer of the flex cable. This conductive plate can then be attached to a ground potential, in a manner that will be subsequently described.
In use, the flex cable may be arranged to extend down the front of the carrier (i.e., on the side the die chip is disposed), and then flexed and bent to pass between the feet of the carrier and through the space therebetween. Thus, the conductive plate will then be disposed in a region behind the carrier.
In a further exemplary aspect of the invention, the optical transceiver arrangement further includes a laminate assembly. The laminate assembly includes a printed circuit board or wiring board, that has a plurality of superposed, alternating conductive layers and insulating layers formed in discrete planes. A front surface of the wiring board may have various electronic components, such as a light emitter driver chip and/or light detector driver chip, attached thereto, and may have electrically conductive pathways or wirings (also known as traces) between the components. The driver chips may be positioned so that in the final optical transceiver arrangement, the driver chips are positioned away from the carrier to aid in heat dissipation.
The wiring board can be adapted to allow it to be attached to a further printed circuit board, for example, by an end user. By way of example, the lower surface of the wiring board can be provided with a plurality of conductive pads arranged in an array, each of which is coupled to a ground plane, power plane and wiring plane of the board, using vias, for example, and each of which may be attached to a respective lead of the further printed circuit board using ball grid array (BGA) technology.
The laminate assembly may further include a polymer coating disposed on the upper surface of the wiring board, and upon which the housing portion can be disposed. The polymer coating may be relatively thick, and formed to provide locating features to facilitate the positioning of the various other subassemblies. For example, the housing portion may be provided with one or more projecting pins on a lower surface thereof, and the polymer coating may be provided with receiving holes that accommodate the respective projecting pins. Thus, during manufacturing, the housing portion can be quickly located on the laminate assembly in the desired location. Moreover, the coating protects the wirings and components on the surface of the wiring board, and helps to distribute heat generated by the drivers over a larger surface area.
Moreover, the polymer coating may be provided with one or more recesses formed therein, to expose respective conductive pads that are electrically coupled to the ground plane. The feet of the carrier can then be electrically bonded, using an electrical epoxy for example, to the conductive pads so that the carrier is electrically coupled to the ground plane. Moreover, the conductive plate of the flex cable may be electrically bonded to another conductive pad, to provide another means of electrically coupling the ground plane to the die chip and carrier. Further, the signal wires of the flex cable may be coupled, for example wire bonded, to respective signal traces on the surface of the laminate. Thereafter, the various electrical connections can be coated to protect the connections and wires from being damaged. For example, the coating can be a socalled chip coat epoxy material.
During the coupling of the flex cable to the laminate assembly, the housing portion may also be fixed to the laminate assembly. For example, the housing portion may be epoxied to the laminate assembly.
In another exemplary aspect of the invention, the optical transceiver arrangement may include a heat sink cover disposed over the laminate assembly. In this exemplary aspect of the invention, the polymer coating may include a step arranged around an outer periphery thereof, and the heat sink cover may have a flange that engages with the step to position the heat sink cover relative to the laminate assembly. Once in position, the heat sink cover can transfer and dissipate heat generated by the drivers, for example.
The heat sink cover may also be provided with a downwardly-projecting finger that is adapted to engage with an exposed conductive pad of the wiring board, which is coupled with the ground plane. In this manner, when the heat sink cover is in position, the heat sink cover will be electrically coupled with a ground potential, allowing the heat sink cover to serve as a further ground potential for the light emitter/light detector. Moreover, the downwardly-projecting finger can be positioned to extend between adjacent housing portions (when so provided), and in particular between the respective light emitter and light detector when so provided, to serve as an electromagnetic emissions separator. Thus, the heat sink cover can help prevent electromagnetic interference from occurring between the light emitter and light detector.
When properly positioned, the heat sink cover may be bonded in place, for example using an epoxy, and may be positioned to abut against a back of the retainer assembly.
The present invention results in an optical transceiver arrangement in which various delicate components are sealed and protected. Moreover, the thermal characteristics are optimized, resulting in increased efficiency. Further, optical clarity is enhanced and the resulting structure can be easily assembled and used in small spaces. Further, the arrangement allows for both a transmitter and detector in the same package. Additionally, this arrangement allows MPO and MTP optical connectors to be selectively attached thereto. Further, the resulting optical transceiver arrangement has fewer parts, thus reducing inventory and reducing manufacturing time. Moreover, due to the elimination of a separate optical coupler, the reliability of the resulting structure is enhanced, since the optical coupler portion cannot shift or become separated from the housing portion, or become damaged during assembly.